I 've been working out the bugs with this '04 YZ450F and I now have it running correctly after replacing the carb, setting the valves corretly,installing the correct hot mechanism and fixing a grounded neutral switch but after I took it out for it's 1st ride ( I had previously changed the oil since I had to replace the water pump seals) and then changed the oil for the 2nd time, it was blacker than I remember seeing any of my other YZ thumpers. I also had installed a new oil filter and it had alot of crap in it; it wasn't packed but more than I would expect from only 1 ride. We rode the bike for about 1.5 hours on a tight MX track. The bike does have some time on it; it was raced/ridden by a pro off road guy so I am thinking that maybe the cam chain guides are toast among other things? Any ideas as to why the oil would be black after only 1.5 hrs of riding?